Most of us brew the way we cook, which is to say, with gas or electricity. When we’re just starting out with extract kits, we use whatever we have at hand, usually the kitchen stove. Moving up to larger batches or bigger boils often entails a move to an outdoor propane burner, and those who really dive in use sophisticated brew rigs that commonly rely on propane, natural gas, or electricity for heat.
While gas and electricity differ in how they create heat, they’re united in the manner in which they deliver it. Both rely on direct contact with some kind of heat source, a phenomenon scientists call conduction. In the case of gas, a flame heats the kettle (along with the surrounding air), which in turn heats your wort. Electric brewing typically involves direct contact between an electric heating element and water or wort, a combination that necessitates the utmost in safety precautions.
But there’s another way to heat wort that doesn’t get as much attention: induction. Unlike gas and electric methods, which depend on the direct transfer of heat from a source, through the kettle, and to the wort, induction turns the kettle itself into the heat source. There’s no middleman.
You see, an induction burner isn’t really a burner at all. An induction element draws electricity from your household power source and directs the current through a tightly wound copper coil. This induces a magnetic field (remember Faraday’s Law of Induction from physics class?), which, in turn, excites the individual molecules of ferromagnetic material (such as stainless steel) within your cookware, causing them to vibrate. This atomic-level vibration generates heat, which is what warms the pot and, consequently, the wort within.
Because there’s no direct heat source, induction is incredibly efficient: Virtually all of the generated heat goes right into that which is to be heated. So why isn’t induction heating more popular among homebrewers? It largely comes down to power.
The largest standalone induction burners commonly available in North America deliver 1,800 watts because that’s about all that you can draw from a single 120-volt outlet without throwing a breaker, assuming a typical 15 amp household circuit. These 1,800-watt burners are sufficiently powerful to bring 4 gallons (15 liters) of wort from steeping temperature to a boil in a reasonable amount of time, about 20 minutes (count on another half hour to get room temperature water to steeping temperature). Small-batch all-grain brewers and those who brew from extract may find that these kinds of burners fit the bill nicely.
If you want to perform a full boil, however, you’ll have to start with roughly 6.5 gallons (25 liters) of wort to end up with 5 gallons (19 liters) after an hour. In this case, 1,800 watts is a little undersized. It’s partly for this reason that induction hasn’t caught on, particularly among all-grain brewers: It can take almost 40 minutes to raise 6.5 gallons of wort from mash temperature to boiling if you only have 1,800 watts.
If you’re lucky enough to have a 220–240 volt outlet, though, then you may be able to use standalone burners of up to 3,500 watts or more, which are beefy enough to let you boil those larger volumes within a reasonable timeframe. And if your kitchen range happens to be an induction unit, then you may already have an element of more than 3,500 watts at your disposal, perfect for full batches of all-grain wort.
But there’s another issue, aside from power. An induction cooktop is usually made of glass, and the weight of so much liquid (not to mention the large stainless kettle) could very well crack it. But—and this is the beauty of the technology—induction doesn’t require direct contact between the burner and the pot. Thus, if you can safely support the kettle above the induction element with some kind of non-magnetic, heat-resistant frame, you can protect the glass cooktop and still gain the benefits of this fascinating approach to brewing beer.
Finally, if you want to give induction a try, remember that you have to use a kettle made from a ferromagnetic material such as stainless steel. Aluminum and copper won’t cut it. The easiest way to tell? Just see if a magnet sticks to the bottom of the pot. If it does, you’re ready to go.